The present invention is directed to a dental spray hand piece having an agent line leading through the hand piece and terminating in a spray nozzle, a valve arrangement for controlling the flow of an agent in the line which valve arrangement is actuated by a purchase. The agent line also includes an arrangement for preventing dripping when the valve closes or stops the flow in the line and this arrangement creates a suction on the agent in the line adjacent to the nozzle to draw the agent back from the end of the nozzle.
A turbine hand piece, which has return feed means for fluid disposed outside of the hand piece, is disclosed in German Patent No. 1,077,379. The return feed means creates an automatic reflux or suction of the remaining fluid present particularly in the area of the fluid discharge after the fluid feed has been shut off or stopped and this return feed means utilizes a diaphragm. However, such a return feed means or device is relatively large in structural terms. The device also requires an additional control agent such as compressed air for displacing the diaphragm or requires an electromagnet for displacing the diaphragm.
U.S. Pat. No. 4,149,315 discloses a spray hand piece wherein the valve and return feed means are disposed in the hand piece itelf in the form of a spring-loaded piston actuated by the purchase. Such a structure, however, is relatively complicated and involved because of the small parts and the tight tolerances. Moreover, given the accumulation of dirt or respectively given wear of the piston sealing rings, such a device tends to leak and to drip the agent at the discharge location which is undesirable in dental preparation technology.
Another known spray hand piece is disclosed in U.S. Pat. No. 1,556,181. In this hand piece, the agent flows through a pinchable hose section and a rocker arm mechanism is provided for controlling the flow in the hose section. A spring presses the rocker arm with a pressure element against the hose so that it becomes pinched to such a degree that the agent flow in the hose section is stopped. When the purchase is depressed, this moves the rocker arm to a position to remove the pinching of the hose section. A disadvantage of such a hand piece is that the spray agent such as water can drip after the valve is closed. This dripping is even promoted by pinching the hose since the water is displaced due to the pinching operation and thus the water situated between the valve and the nozzle is pressed toward the nozzle discharge or end.